1. Technical Field
This invention relates generally to hydraulic fluid supply systems for operating high pressure transmissions of vehicles.
2. Related Art
In a typical high pressure supply system for an automatic transmission, an oil pan is mounted below the transmission to contain a supply of hydraulic transmission fluid. A hydraulic pump is housed in the pan and has an outlet communicating with an inlet of the transmission. Also housed within the pan below the pump is a filter device which includes a housing having an outlet communicating with the pump and an inlet communicating with the source of fluid in the pan. The pump draws fluid from the pan through the filter and delivers it to the transmission.
It is important in such systems that fluid be maintained in the system even when the vehicle is not in operation. If pressure is lost due to an air leak in the transmission, it would allow for some or all of the fluid to drain back into the pan. Once the fluid is drained, it can take some time for the system to restore sufficient pressure to operate the transmission, during which time the vehicle would be disabled. Losing line pressure can also cause damage to the pump if allowed to run dry or at low pressure for an extended time.
It is difficult to build a transmission that is completely air tight.
It is an object of the present invention to overcome the loss of fluid problems associated with the occurrence of air leaks.
A hydraulic system constructed according to a presently preferred embodiment of the invention for operating a transmission of a vehicle comprises a hydraulic pump having a fluid inlet for drawing hydraulic transmission fluid into the pump and a fluid outlet for expelling the fluid under elevated pressure from the pump to the transmission. The system also includes a source of the hydraulic fluid and a filter device having a filter housing provided with an inlet which communicates with the fluid source and an outlet which communicates with the inlet of the pump. The system also includes a check valve which is operative to permit one way flow of the fluid in the system.
The invention further contemplates a transmission filter assembly for such a system which comprises a housing having a fluid inlet for communicating with the source of hydraulic fluid, a fluid outlet for communicating with a pump, and a filter medium disposed within the housing between the inlet and outlet for filtering fluid passing through the housing. The assembly includes a check valve communicating with the inlet of the filter housing to permit one way flow of fluid into the filter housing through the inlet.
The invention provides a simple, low cost solution to solving the problems associated with air leaks in a high pressure fluid supply system for a transmission of an automotive vehicle. The check valve permits fluid to flow through the system and to be supplied to the transmission for its operation, but blocks reverse flow of the fluid. In the event the transmission develops an air leak which would normally cause the fluid to drain back into the transmission oil pan, the check valve operates to stop such back flow during periods when the supply system is not actively supplying fluid for operating the transmission (e.g., when the engine of the vehicle is not running). Thus, the system of the invention is immune to the problems normally encountered with high pressure transmissions that are prone to leaking air into the fluid supply system.
The invention has the further advantage of maintaining the hydraulic pump in a primed state and ready at the start-up of the vehicle to immediately supply sufficient fluid pressure to the transmission for its operation, regardless of whether or not the transmission has or has not developed an air leak. Maintaining the pump in a ready state independently of the air-tight integrity of the transmission has the advantage of providing better overall performance of the system because it is insensitive to the integrity of the sealing of the transmission. Maintaining the pump in a primed ready state has the further advantage of prolonging the expected operating life of the pump by lessening the demand on the pump to restore high pressure conditions in the event of a transmission air leak. Maintaining the pump in a primed ready condition assures that the pump does not run dry which can damage or destroy a hydraulic pump.
The invention has the further advantage of simplifying the solution to the problem of air leaks and high pressure transmissions by providing the subject supply system outfitted with the check valve which enables the system to operate in connection with virtually any transmission, making it adaptable for solving virtually any performance problems associated with transmission air leaks.